Sound recording and reproducing element, and more particularly a permanent magnet therefor



v 1 y 1939- c. scHAARwAcHTER El AL I 2.167.1 8

SOUND RECORDING AND REPRODUCING ELEMENT, AND MORE PARTICULARLY A'PERMANENT MAGNET THEREFOR Filed Feb. 26, 1937 A 2 Sheets-Sheet 1TEMPERHTUR E C BY flLB/q/Y RUPPELT ATTORNEY.

Search Room 2,167,188

2 Sheets- Sheet 2 CROSS REFERENCE C. SCHAARWAC HTE R ET.A1

PARTICULARLY A PERMANENT MAGNET THEREFOR Filed Feb. 26,

SOUND RECORDING AND REPRODUCING ELEMENT, AND MORE 0 a a 9 a m a M M w wm a M m l/ 0 2 0o a m 5 m 4 R 0W \L 4 [III] R .9 w A ww J m g 4 m w 3 oa o o w o a 0 o 9 1 0 a w 2 2 2 2 w m w M MACHINE ELEMENTS AND MECHAMSMS7'00 800 .900 /OO(} TEMPERATURE C JNVENTOR. C/YFL SC'H/IARWHCHTER BY fiLBAN FPO/ PEL T ATTORNEY.

Patented July 25, 193

UNITED STATES PATENT orrics UND decal-si a; I

Carl Schaarwach r and Alban Ruppelt, Altena,

Germany, assignors to Vereinigte Deutschev MetallwerkeAktlengesellschaft, Frankforton-the-Mai -Heddernheim, Prussia, Germany,a corporation of Germany Application February 26, 1937, Seriall\lo.'12'1,810- In Germany March 2, 1936 1?. Claims. (Cl. arc-41.4

cial heat-treatment and subsequent magnetizing treatment producesurprisingly new permanent magnets, possessing a relatively highcoercive force. It.has been found that the high coercive to two dominantcritical factors.

REPRODUCINi The present invention relates to a sound recording andreproducing element, and more particularly to a permanent magnettherefor.

Heretoiore various proposals have been made 5 in the sound reproducingand recording art to utilize metallic strips, wires, and other elementsand subsequently reproduc ing. Among the outstanding applications ofthese proposals may be mentioned devices for recording and reproducingdictation, phonographic records, automatic telephone call receivingsystems, and talking motion pictures. The investigators in this art weresearching for a metallic permanent magnet which could .be made incommercial quanindustrial basis and which possessed requisite propertiesincluding ductility, workability and uniformity. During the early detouse The first Y saturation of the alpha iron crystals with nickel Thesecond factor is the production by a special re-heating operation toproduce a fine dispersion oi'sub-microscopic segregations of mixedcrystals composed substantially entirely of copper and nickel. Theunusually fine dispersion which is obtained is probably due to aphenomenon known as lookerstellen or of loose spots in the crystallattice. The phenomenon of lockerstellen is due to the transformation ofgamma iron crystals to alpha iron crystals at temperature below that ofrecrystallization of the present special alloy.

It is an object of the invention to provide an improved sound recordingand reproducing apparatus especially one provided with a novel uniformalloy steel'strip or wire or element which is an emcient permanentmagnet and which records sound accurately and which eiiectivelyreproduces the recorded sound even after considerable periods of time.

A further object of the invention is the provifor producing permanentmagspecial alloy steels containing tical for successful commercialoperations. more recent years proposals have been made to use cobaltsteel, but cobalt steel shortcomings, including non-uniformity, cost,and the like. Endeavors have been made to provide the art with better,more uniform and cheaper permanent magnets which were composed of ametal or alloy which could be manulectured on a commercial basis andwhich possessed the unusual combination 01 properties renets made fromquired in this art. us, Swiss Patent No. 127,077 describes a magnetwhich is soft an critical percentages of copper and of nickel. whichdoes not retain anysubsequent amount of It is also within the contemp ofthe a soft magvention to provide a process of producing peralloy steelswhich are subjected to special heat treatment for the improvement oiproperties especially the coercive force and residual magnetism and thesubsequent magnetization by treatment with a magnetizing force.

Other objects and advantages oi the invention will become apparent fromthe following description taken in conjunction with the accompanyingdrawings in which- Fig. 1 is a diagrammatic view of the improved soundrecording and reproducing apparatus; Fig. 2 depicts a graph illustratingthe hardness and the coercive force of the present in a soit and in ahard condition to various temperatures in comparison h a steel alloy notpossessing the critical composition of the present permanent magnet;

, Fig. 3 is a graph illustrating another embodiment oi the presentpermanent magnet and residual magnetism. As is known, net can bemagnetized with a relatively low magnetizing force, but immediatelyloses its magnetism when the magnetizing force is discontinued. Otherpatents and publications including United States Patents Nos. 1,803,353,1,805,049, 1,853,575, and 1,992,325, describe alloys some of which maypossess properties hich may have w made them useful as soft magnets, butnone of se would have been useful as permanent magnets for soundrecording and reproducing systems. Although various attempts andproposals have been made, none, as far as is known, has successfully andfully solved the problem and provided the art with a completelysatisfactory permanent magnet for sound recording and reproducingpurposes.

We have discovered, a permanent magnet which has special utility for useas .a sound recording and reproducing element. It has been found thatspecial iron, nickel, copper alloys having critical narrow ranges whensubjected to a spe- Brinellwhich effects a uniform magnetization of bandI throughout its full length. Coils 'I and 8 are connected with anamplifier 9, which amplifies the sound currents produced by a microphoneN which is exposed to the efiect of the sound oscillations to berecorded. Generally speaking, it is preferred to provide a preliminarymagnetization of the recording coils by means of a weak electric currentderived from a source ii. Coils l2 and 43 are connected with a secondamplifier H which amplifies the incoming weak electrical currents andintroduces them into a loudspeaker i5.

From the preceding description, the operation of the magnetic soundrecording and reproducing system will be readily understood by thoseskilled in the art. Special alloy steel band i is passed at a uniformspeed of say about 1.5 meters per second, between thetwo recording coils1 and which are arranged opposite to each other and are displaced withrespect to each other by about 0.25 to about 0.50 mm. The two coils areconnected in series and constitute the so-called recording head which-islightly pressed by means of a spring against the moving band i. The

sound waves received by the microphone are converted into electricaloscillations and are amplified by the amplifier. The band passingthrough the recording head is thus magnetized in accordance with theseelectrical oscillations. When it is desired to reproduce the soundrecorded on the band, a second system of coils l2 and I3, the socalledreproducing head is subjected to the effect of the magnetic fieldproduced by the band whereby an alternating electro-motive force will beinduced in the reproducing coils l2 and 13. This alternatingelectro-motive force may be amplified by'a suitable amplifier and theamplified currents are introduced into a loud speaker l or some othersound producing means whereby the original sound oscillations recordedon the band will be reproduced.

In order to obtain reproduction substantially free from distortion andthereby effect substantially perfect reproductionof the original sound,a pre-magnetizing head constituted of coils 4 and 5' is arranged inproximity to the band i. This premagnetizing head causes strong anduniform magnetization of the band up to'practically the maximummagnetism. By means of the unusually strong residual magnetism in theband and by means of employing a suitable negative biasing voltage inthe recording coil, it is possible to so adjust the alternating magneticfield that the recording is carried out upon the most favorable andlinear part of the hysteresis curve as those skilled in the art willreadily appreciate.

According to the present invention the novel sound recording andreproducing element and permanent magnet therefor is made of aspecialductile alloy steel consisting of about 70% to about 87% of iron, aboutto about of nickel and the balance substantially copper and constitutedofalpha iron crystals super-saturated .has a greater solubility withcopper and nickel and having a. gamma alpha transformation at atemperature below the re-crystallization temperature of said alloy andhaving an alpha-gamma transformation at a temperature higher than saidgamma-alpha trans 5 formation temperature. The band may have in practicea cross-section of about 0.08 x 3 mms. Instead of the band, it ispossible to use wire with about 0.22 mm. diameter. For best resultstheinvention'contemplates as a new article ofmanu- 1o facture', a soundrecording and reproducing element elongated by working and made ofa'permanent magnet, comprising a ductile alloy consisting of about 70%to about 87% of iron, about 10% to about 20% of nickel and the balancesubstantially 15 copper and constituted of alpha iron matrixsupersaturated with copper and nickel and containing a finedispersion ofsubmicroscopic segregation of mixed crystals composed substantially ofcopper and nickel.

The present special alloy steelsmay be mechanically treated in thehomogenized soft condition to an unusually high degree. Actual testshave demonstrated that the special steel alloys may be rolled. to stripor drawn to wires and show between the new critical composition limitssurprisingly high permanent-or residual magnetism.

It was discovered that special steel alloys whose critical limits areabout 70% to about 87% iron; about 3 to about 20% copper, and about 10to 80 about 20% nickel acquire unexpected permanent magnetic qualitiesaftena special'treatment-involving heating and subsequent magnetization.These special steels consist of iron as a base and two additionalcritical metals present in critical 86 percentages. The one metal iscopper which is in part not miscible with the iron and the second isnickel which forms not only mixed crystals in all proportions withiron',but also forms a solid solution with the copper which supersaturates 40the alpha iron upon a special heat treatment. The nickel also effects atemperature hysteresis of the gamma alpha transformation whichhysteresis increases with increasing amounts of iron.

From a. theoretical point of view the binary iron-copper system showsthat the gamma iron for the copper than the alpha iron. In the eventthat nickel is present, more copper and nickel would be dissolved in thegamma iron than in the alpha iron. With alloy steels having compositionsoutside of the present critical ranges, the transformation of gamma ironinto alpha iron occurs at higher temperatures at which a change of theplaces of the atoms in the lattice structure is effected. A part I551vof the copper iron and of the nickel' would then precipitate and causeobjectionable segregation which is undesired. These detrimentalsegregations would coagulate into larger particles and would beincapable of effecting the improvement 6 of the coercive power ascontemplated by the present invention. If, on the other hand, thegamma-alpha transformation occurs as in the present invention attemperatures below the recrystallization temperatures of the specialsteel 6 alloys, say, for instance,.at temperatures below 300 C., thenthere will be obtained highly supersaturated crystal lattices of alphairon due to the freezing of the atom movements.

It was discovered that within these fields the coercive power andresidual magnetism after homogenising, -quenching and heating the alloysto a temperature up to somewhat above those used for precipitatinghardening are rather high.

The special heat-treatment of the present steel 76 alloys is, accordingto the principles of the present invention, thefollowing novelcombination of operations. At first, it is necessary to homogenize thealloys by annealing them at a temperature within the homogenizationlimits. That is at temperatures above 900 C., say, for instance, at

a temperature of about 1000 C. .After this annealing, the alloys arequenched in order to preserve the homogenized structure at lowertemperatures. After the quenching, the alloys may be worked, say rolledor drawn. etc., and the alloys are re-heated to a temperature within theirreversible region extending from the gammaalpha transformationtemperature to the alphagamma transformation temperature. This reheatingis preferably conducted at a temperature above those temperaturesheretofore employed for conventional hardening. If reference is made toFig. 3, this special relation will be clearly appreciated. It was foundthat by only using the foregoing reheating operation the highestcoercive forces could be produced in the present steel alloys. The mostuseful temperature is just be low the upper temperature limit of theirreversible transformation field, that is about 650 C.

Furthermore, there will be developed a phenomenon known asgitterlockerstellen" during the gamma-alpha transformation. By thenincreasing the temperature, a segregation in the form of a very finedispersion of sub-microscopic particles composed substantially ofnickel, iron and copper will progress at the loose spots of the latticestructure.

There are accordingly two dominant and critical factors which make itpossible to obtain a high coercive force in the present special steelalloys. high over-saturation of the alpha iron crystals in consequenceof homogenising and quenching these alloys having the gamma-alphatransformation at relatively low temperatures. The other or secondfactor is the segregation caused by reheating in a very fine form of thesubmicroscopic nickel-copper crystals due to the lockerstellen. Thecopper content, therefore, has to be maintained between the criticalpercentages of about 3 to about 20%, the iron content from' about 70% toabout 87%, and the nickel content from about 10% to about 20%.

For the purpose of giving-those skilled in the art a betterunderstanding of the invention, the

following illustrative examples are given.- In Fig.

, 2 are shown the qualities of two alloys, numbered 53 and 26 after thesame heat treatment. The 4 compositions of these alloys are as follows:

Alloy No. 53 has a composition according to the invention, whilst alloyNo. 26 has a composition beyond the critical limits contemplated by theinvention. Alloy No. 26 has only a maximum of coercive power of about3.0 oersteds. The alloy 53 has a remarkable coercive power up to 85oersteds. The maximum coercive power of alloy 53 is reached afterheating to 600 C., whilst the maximum coercive power of alloy 26 isreached only at 800 C.

In addition, the quality index, [BxH] main/81, within the irreversiblefield increases with increasing nickel content, and somewhat with in-CROSS REFERENCE One of these factors is the extremely Search creasingcopper content. The diagrams depicted in Figs. 2 to 4 show the maximumcoercive power for various nickel contents. The composition of thealloys is the following:

Fe Ni Cu li max.

Percent Percent Percent Oersteds A further illustrative example is thealloy containing 75% iron, 15% of nickel, and of copper. This alloy,after the above-mentioned heat-treatment has 200 oersteds, 6000 gauss,an energy [BXH] max. of 533,000; and a quality index [BXH] max./81r of21500. The alloy containing 77.5% iron, of nickel, 7.5% of copper, has150 oersteds; an energy of 400,000; and a quality index of 16,000. Thisalloy may be easily and readily worked hot and cold.

An illustrative example for the production of sound recording andreproducing wires is the following: The alloy with 75% iron, nickel, and5% copper is melted and hot-rolled down to about 6 mms. wire in theusual manner. Then it was pickled and cold drawn to 2.2 mms. Now thewire was annealed in an annealing furnace, at a temperature of about 900C. to 1000 C. in a hydrogen atmosphere. The wire then was cold drawn to1.2 mms. and annealed again inthe foregoing manner. The wire was colddrawn to the finer diameter of 0.22 mm. Now, in order to give it themagnetic hardening, the wire was slowly heated in an annealing furnacefor about seconds at 515 C. The thus-treated wire had the followingqualities: tensile strength of 152 kilograms/mmfi; elongation of 0.5 to1%, coercive power of oersteds; and a residual magnetism of 6000 gauss.

The special heat treatment consists in successive re-heatings atslightly increased temperatures followed each time by quenching inwater. Thus, for instance, the material was heated onehalf hour to 500C., quenched in water, and then re-heated another halfhour at 650 C.With this process, the highest magnetic effects may be obtained.

Cobalt may be substituted for iron to some extent. The percentage ofcobalt should not be higher than about 20%, so that iron is alwayspresent to more than 50%. Y

The nickel may be substituted in part or fully by manganese, platinum,or palladium, and the copper may be substituted by .gold. All thesesubstitutes have practically the same effect on the structure of theiron and, therefore, on the magnetic qualities as nickel, or copper,respectively.

Small amounts of additional auxiliary metals, as, for instance, aluminumup to 3%, vanadium, chromium, or molybdenum up to 10%, may be presentwithout materially changing the aforesaid qualities and results.

It is claimed:

1. As a new article of manufacture an elongated sound recording andreproducing element having a worked structure and capable of being.permanently magnetized, comprising a ductile alloy consisting of about70% to about 87 of iron, about 10% to about 20% of nickel and thebalance substantially copper and constituted of alpha iron crystalssuper-saturated with copper and nickel and having a gamma-alphatransformation at a temperature below the recrystallization temperatureof said alloy and having an alpha-gamma transformation at a temperaturehigher than said gamma-alpha transformation temperature.

2-. As a new article of manufacture, an elongated sound recording andreproducing element having a worked structure andcapable of beingpermanently magnetized, comprising a ductile alloy consisting of about70% to about 87% of iron, about 10% to about of nickel and the balancesubstantially copper and constituted of alpha iron matrixsuper-saturated with copper and nickel and containing a fine dispersionof sub-microscopic segregations of mixed crystals composed substantiallyof copper and nickel.

3. As a new article of manufacture, an elongated sound recording andreproducing element having a worked structure and capable of beingpermanently magnetized, comprising a ductile alloy consisting of about70% to about 87% of iron, about 10% to about 20% of nickel and thebalance substantially copper and constituted of alpha iron crystalssuper-saturated with copper and nickel and having a gamma-alphatransformation at a temperature below the recrystallization temperatureof said alloy and having an alpha-gamma transformation at a temperaturehigher than said gamma-alpha transformation temperature, said alloyhaving been sub jected to heat-treatment involving heating to atemperature aboout 900 C., quenching the thus heated alloy andre-heating the quenched alloy to a temperature of about 500 to 650 C..

4. As a new article of manufacture, an elongated sound recording andreproducing element having a worked structure and capable of beingpermanently magnetized, comprising a ductile alloy consisting of about70% to about 87% of iron, about 10% to about 20% of nickel and thebalance substantially copper and constituted of alpha iron matrixsuper-saturated with copper and nickel and containing a fine dispersionof sub-microscopic segregations of mixed crystals composed substantiallyof copper and nickel, said alloy having been subjected to heat-treatmentinvolving heating to a temperature above about 900 C., quenching thethus heated alloy, cold-working said quenched alloy, and re-heating thequenched alloy to a temperature of about 500-to 650 C. v

5. As a new article of manufacture, an elongated sound recording andreproducing element having a worked structure and capable of beingpermanently magnetized, comprising a ductile alloy consisting of about75% iron, about 20% nickel, and about 5% copper and constituted of alphairon crystals super-saturated with copper and nickel and having agamma-alpha transformation at a temperature below the recrystallizationtemperature of said alloy and having an alpha-gamma transformation at atemperature higher than said gamma-alpha transformation temperature.

6. As a new article of manufacture, an elongated sound recording andreproducing element having a worked structure and capable of beingpermanently magnetized, comprising a ductile alloy consisting of about78% iron, about 16% nickel, and about 0.5% copper and 0.5% manganese andconstituted of alpha iron crystals super-saturated with copper andnickel and having a gamma-alpha transformation at a temperature belowthe recrystallization temperature 01 said alloy and having analpha-gamma transformation at a temperature higher than said gamma-alphatransformation temperature.

7. As a new article of manufacture, a worked permanent magnet made of analloy consisting of about 70% to about 87% iron, about 10% to about 20%nickel and the balance substantially copper with minor impurities andconstituted of alpha iron crystals super-saturated with copper andnickel and having an alpha-gamma transformation at a temperaturesubstantially above 300 C., said alloy having a substantially permanentcoercive force of more than about oersteds, and having been subjected toheattreatment involving heating to a temperature about 900 C., quenchingthe thus heated alloy and re-heating the quenched alloy to atemperature'of about 500 to 650 C.

8. As a new article of manufacture, a worked permanent magnet made of analloy consisting of about 70% to about 87% iron, about 10% to about 20%nickel and the balance substantially copper with minor impurities andconstituted of alpha iron crystals super-saturated with copper andnickel and having an alpha-gamma transformation at a temperaturesubstantially above 300 C., said alloy having been subjected toheat-treatment involving heating to a temperature above about 900 C.,quenching the thus heated alloy and re-heating the quenched alloy to atemperature of about 500 to 650 C., and said alloy having asubstantially permanent coercive force of more than about 30 oersteds.

9. Asa new article of manufacture, a worked permanent magnet made of analloy consisting of about 70% to about 87% iron, about 10% to about 20%nickel and the balance substantially copper with minor impurities andconstituted of alpha iron crystals super-saturated with, copper andnickel and having an alpha-gamma transformation at a temperaturesubstantially above 300 C., said alloy having been subjected toheattreatment involving heating said alloy to repeated heatings abovethe temperature of recrystallization but not higher than the alphagammatransformation temperature, said repeated heatings increasing intemperature, quenching the alloy after each heating, coldworking saidquenched alloy, and re-heating the quenched alloy to a temperature ofabout 500 to 650 C., and said alloy having a substantially permanentcoercive force of more than about 30 Oersteds.

10. The process of producing an easily workable permanent magnet made ofan alloy consisting of about 70% to about 87 of iron, about 10% to about20% of nickel, and the balance substantially copper, and having a highhysteresis of the gamma-alpha transformation which comprises heatingsaid alloy to a temperature higher than about 900 (1., quenching thethus heated alloy whereby a uniform structure constituted of alpha ironcrystals super-saturated with copper and nickel is produced, reheatingsaid quenched alloy to a temperature between the alpha-gammatransformation temperature and the gammaalpha transformationtemperature, and subse-' quently subjecting the thus heat-treated alloy.

to a magnetizing force whereby a permanent magnet is produced having acoercive force of at least 30 oersteds.

11. The process of producing an easily workable permanent magnet made ofan alloy consisting of about to about 87% of iron, about 10% to about20% of nickel, and the balance substantially copper, and having a highhysteresis of the gamma-alpha transformation which comprises heatingsaid alloy to a temperature higher than about 900 C., quenching the thusheated alloy whereby a uniform structure constituted of alpha ironcrystals super-saturated with copper and nickel is produced, subjectingthe quenched alloy to repeated reheating at successively increasingtemperatures higher than the transformation temperature to below thealphagamma transformation temperature, quenching the re-heated alloyafter each re-heating, and subsequently subjecting the thus heat-treatedalloy to a magnetizing force whereby a permanent magnet is producedhaving a coercive force of at least 30 oersteds.

12. The process of producing an easily workable permanent magnet made ofan alloy con sisting of about 70% to about 87% of iron, about 10% toabout 20% of nickel, and the balance subgamma-alpha stantially copper,and having a high hysteresis of the gamma-alpha transformation'whichcom-.

alloy whereby a uniform structure constituted of alpha-iron crystalssuper-saturated with'copper and nickel is produced, cold-working saidquenched alloy, subjecting the quenched alloy to repeated re-heating atsuccessively increasing temperatures higher than the gamma-alphatransformation temperature to below the alphagamma transformationtemperature, quenching the re-heated alloy after each re-heating, andsubsequently subjecting the thus heat-treated alloy to a magnetizingforce whereby a permanent magnet is produced having a coercive force ofat least 30 oersteds.

CARL SCHAARWACHTER.

ALBAN RUPPELT.

